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  1. #1
    Join Date
    Dec 2007

    Default Vapor Barrier Confusion


    Thank you for this forum!!

    I am remodeling my bathroom and I have a few questions regarding installing a vapor barrier on the exterior walls that run along a three-wall alcove bathtub. The wall spaces (2x6) are insulated with unfaced, fiberglass batt insulation. My plan is to install a 6mil plastic sheet vapor barrier on the exterior walls, over the unfaced insulation. Then, I plan to install 1/2" hardibacker cement board inside the bathtub wall areas, directly onto the wall studs, and then install ceramic tile. My question is in regards to how the plastic vapor barrier should be installed on the exterior walls that run along the bathtub. I have attached a file with hand drawings that illustrate three options for installing the plastic vapor barrier.

    Option 1 has two sheets of poly installed on exterior wall; one sheet above tub where the bottom of the sheet extends over the bathtub lip, and the second sheet runs from the floor up a few inches above the bathtub lip. This would leave a seam between the two overlapping sheets.

    Option 2 has just one sheet of plastic that runs from the ceiling to the floor - no seams. Concern: any moisture that condenses on the sheet will run behind the tub, onto the floor.

    Option 3 has a seamless sheet that runs from the floor to the ceiling. And then another sheet is installed on the wall from the ceiling to the bathtub lip, where the bottom of the sheet overlaps the bathtub lip.

    I'm at a loss with what option would be most appropriate.
    My concerns are of course moisture penetration into the walls spaces and behind the bathtub.

    Any thoughts or suggestions would be greatly appreciated!!

    Mark (Western New York)
    Note: I posted this same thread in Interior - General Section. I posted it there and then found this section to be more appropriate for this question.
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